Electrochemical cell designs are classified as undivided when the solution being electrolyzed freely flows past the anode and the cathode or as divided when the cathode and the anode are separated from each other by an ion-permeable membrane which inhibits mixing of the solution which contacts the cathode (catholyte) and that which contacts the anode (anolyte). Though simple in concept, in practice divided cells suffer disadvantages relative to undivided cells. The first is the necessity of a dividing ion-permeable membrane, which increases the total cell voltage, introduces stability, poisoning, pressure differential and temperature limitations that can require periodic dismantling of the cell in commercial practice. In addition, the two separate solutions to be recirculated increase the required pumping, tankage and piping requirements for a given process. However, the divided cell is typically necessary in situations in which the desired chemistry at the working electrode is adversely affected by contact with the counterelectrode, or by reaction products generated at the counterelectrode. For example, if a reduction at the cathode is electrochemically reversible, the electrons added at the cathode would be removed at the anode, leading to an unproductive redox cycle. Similarly, if a species generated at the cathode is oxygen-sensitive, and oxygen is evolved at the anode, contact with the anode product, oxygen, would be detrimental to the cathodic reduction process.
It would be highly desirable to have a process and cell configuration that can provide the performance benefits of a divided cell configuration in an undivided cell for application to such reaction systems. Applicants invention address this need.